U.S. patent application number 15/754481 was filed with the patent office on 2018-08-23 for attrition-resistant superabsorbent polymer, method for preparing the same and composition for preparing the same.
This patent application is currently assigned to LG Chem, Ltd.. The applicant listed for this patent is LG Chem, Ltd.. Invention is credited to Su-Jin Kim, Young Sam Kim, Bo-Hee Park, Young-In Yang.
Application Number | 20180237611 15/754481 |
Document ID | / |
Family ID | 59283154 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180237611 |
Kind Code |
A1 |
Yang; Young-In ; et
al. |
August 23, 2018 |
ATTRITION-RESISTANT SUPERABSORBENT POLYMER, METHOD FOR PREPARING
THE SAME AND COMPOSITION FOR PREPARING THE SAME
Abstract
The present invention relates to an attrition-resistant
superabsorbent polymer comprising a superabsorbent polymer; water;
and at least three selected from the group consisting of particles
having i) a BET specific surface area of 300 to 1500 m.sup.2/g and
ii) a porosity of 50% or more, a multivalent metal salt, an organic
acid and a polyhydric alcohol, and a preparation method
thereof.
Inventors: |
Yang; Young-In; (Daejeon,
KR) ; Kim; Young Sam; (Daejeon, KR) ; Park;
Bo-Hee; (Daejeon, KR) ; Kim; Su-Jin; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Chem, Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG Chem, Ltd.
Seoul
KR
|
Family ID: |
59283154 |
Appl. No.: |
15/754481 |
Filed: |
November 23, 2016 |
PCT Filed: |
November 23, 2016 |
PCT NO: |
PCT/KR2016/013557 |
371 Date: |
February 22, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 2003/2241 20130101;
A61L 15/425 20130101; C08K 5/09 20130101; C08J 2333/02 20130101;
C08J 2205/022 20130101; C08J 3/075 20130101; C08K 2201/005
20130101; C08K 5/053 20130101; C08J 9/228 20130101; C08K 3/22
20130101; C08K 2003/3081 20130101; C08K 2201/014 20130101; C08K
2201/002 20130101; C08K 3/30 20130101; C08K 3/10 20130101; A61L
15/60 20130101; C08K 2003/2227 20130101; C08K 2201/006 20130101;
A61L 15/24 20130101; C08K 3/04 20130101; C08K 3/36 20130101; C08K
5/092 20130101; C08J 3/24 20130101; A61L 15/18 20130101; A61L 15/20
20130101; C08K 3/36 20130101; C08L 33/02 20130101; C08K 5/092
20130101; C08L 33/02 20130101; C08K 3/30 20130101; C08L 33/02
20130101 |
International
Class: |
C08K 3/36 20060101
C08K003/36; C08J 3/075 20060101 C08J003/075; C08K 3/04 20060101
C08K003/04; C08K 3/22 20060101 C08K003/22; A61L 15/18 20060101
A61L015/18; A61L 15/20 20060101 A61L015/20; A61L 15/42 20060101
A61L015/42; A61L 15/60 20060101 A61L015/60; A61L 15/24 20060101
A61L015/24; C08J 9/228 20060101 C08J009/228 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2015 |
KR |
10-2015-0178269 |
Nov 7, 2016 |
KR |
10-2016-0147386 |
Claims
1. An attrition-resistant superabsorbent polymer comprising: a
superabsorbent polymer; water; and at least three selected from the
group consisting of particles having the following features i) and
ii), a multivalent metal salt, an organic acid and a polyhydric
alcohol: i) a BET specific surface area of 300 to 1500 m.sup.2/g
ii) a porosity of 50% or more
2. The attrition-resistant superabsorbent polymer of claim 1,
wherein the particles are contained in an amount of 0.001 to 2.0
parts by weight based on 100 parts by weight of the superabsorbent
polymer.
3. The attrition-resistant superabsorbent polymer of claim 1,
wherein the water is contained in an amount of 1.0 to 10.0 parts by
weight based on 100 parts by weight of the superabsorbent polymer
and the particles.
4. The attrition-resistant superabsorbent polymer of claim 1,
wherein the organic acid is contained in an amount of 0.001 to 5.0
parts by weight based on 100 parts by weight of the superabsorbent
polymer.
5. The attrition-resistant superabsorbent polymer of claim 1,
wherein the polyhydric alcohol is contained in an amount of 0.01 to
5.0 parts by weight based on 100 parts by weight of the
superabsorbent polymer.
6. The attrition-resistant superabsorbent polymer of claim 1,
wherein the organic acid is at least one selected from the group
consisting of citric acid, oxalic acid, acetic acid, malic acid,
malonic acid, gluconic acid, ascorbic acid, tartaric acid, succinic
acid, lactic acid, fumaric acid and salicylic acid.
7. The attrition-resistant superabsorbent polymer of claim 1,
wherein the polyhydric alcohol is at least one selected from the
group consisting of propylene glycol, monoethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, monopropylene glycol, 1,3-propanediol,
dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene
glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol and
1,2-cyclohexanedimethanol.
8. The attrition-resistant superabsorbent polymer of claim 1,
wherein the particles have a particle size ranging from 2 nm to 50
.mu.m.
9. The attrition-resistant superabsorbent polymer of claim 1,
wherein the particles have superhydrophobicity with a water contact
angle of 125.degree. or more.
10. The attrition-resistant superabsorbent polymer of claim 1,
wherein the particles are at least one selected from the group
consisting of silica (SiO.sub.2), alumina, carbon and titania
(TiO.sub.2).
11. A method for preparing an attrition-resistant superabsorbent
polymer comprising: adding water; and at least three selected from
the group consisting of particles having the following features i)
and ii), a multivalent metal salt, an organic acid and a polyhydric
alcohol to a superabsorbent polymer, thus preparing a hydrous
superabsorbent polymer: i) a BET specific surface area of 300 to
1500 m.sup.2/g ii) a porosity of 50% or more
12. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the particles are contained in an
amount of 0.001 to 2.0 parts by weight based on 100 parts by weight
of the superabsorbent polymer.
13. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the water is contained in an amount of
1.0 to 10.0 parts by weight based on 100 parts by weight of the
superabsorbent polymer and the particles.
14. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the organic acid is contained in an
amount of 0.001 to 5.0 parts by weight based on 100 parts by weight
of the superabsorbent polymer.
15. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the polyhydric alcohol is contained in
an amount of 0.01 to 5.0 parts by weight based on 100 parts by
weight of the superabsorbent polymer.
16. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the organic acid is at least one
selected from the group consisting of citric acid, oxalic acid,
acetic acid, malic acid, malonic acid, gluconic acid, ascorbic
acid, tartaric acid, succinic acid, lactic acid, fumaric acid and
salicylic acid.
17. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the polyhydric alcohol is at least one
selected from the group consisting of propylene glycol,
monoethylene glycol, diethylene glycol, triethylene glycol,
tetraethylene glycol, polyethylene glycol, monopropylene glycol,
1,3-propanediol, dipropylene glycol,
2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol,
polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol,
1,5-pentanediol, 1,6-hexanediol and 1,2-cyclohexanedimethanol.
18. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the particles have a particle size
ranging from 2 nm to 50 .mu.m.
19. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the particles have superhydrophobicity
with a water contact angle of 125.degree. or more.
20. The method for preparing an attrition-resistant superabsorbent
polymer of claim 11, wherein the particles are at least one
selected from the group consisting of silica (SiO.sub.2), alumina,
carbon and titania (TiO.sub.2).
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2015-0178269 filed on Dec. 14,
2015 and Korean Patent Application No. 10-2016-0147386 filed on
Nov. 7, 2016 with the Korean Intellectual Property Office, the
disclosures of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
[0002] The present invention relates to an attrition-resistant
superabsorbent polymer, a method for preparing the
attrition-resistant superabsorbent polymer and a composition for
preparing the attrition-resistant superabsorbent polymer.
BACKGROUND ART
[0003] Superabsorbent polymers (SAPs) are synthetic polymer
materials capable of absorbing moisture about 500 to 1000 times
their own weight. Due to high moisture-absorbing power, such super
absorbent polymers started to be practically applied in sanitary
products, and now they are widely used for preparation of various
products, for example, hygiene products such as paper diapers for
children and adults or the like, water retaining soil products for
gardening, water stop materials for the civil engineering and
construction, sheets for raising seedling, fresh-keeping agents for
food distribution fields, materials for poultice or the like. When
the superabsorbent polymers are used for hygiene products, the
superabsorbent polymers present in diapers may serve to absorb and
maintain urine.
DISCLOSURE
Technical Problem
[0004] Meanwhile, in the course of producing diapers by a
conventional technique, the superabsorbent polymers are subjected
to strong pressure and physical impact. During this process, a
problem arises that due to the attrition of the superabsorbent
polymers, the physical properties are significantly deteriorated,
resulting in the deterioration of performance of the diapers.
[0005] The present invention has been made keeping in mind the
problems encountered in the art, and an object of the present
invention is to provide a superabsorbent polymer having improved
attrition resistance which can exhibit absorbency equal to or
higher than a conventional superabsorbent polymer, and at the same
time, improve an attrition resistance and maintain the improved
attrition resistance for a long period of time, so that when the
superabsorbent polymer is applied to a final product such as
diapers, the deterioration of physical properties due to physical
attrition of the superabsorbent polymer, for example, by
compression or strong air transfer during the production process of
diapers can be minimized, a method for preparing the same and a
composition for preparing the same.
Technical Solution
[0006] In order to achieve the object above, in one aspect of the
present invention, there is provided an attrition-resistant
superabsorbent polymer comprising:
[0007] a superabsorbent polymer;
[0008] water; and
[0009] at least three selected from the group consisting of
particles having i) a BET specific surface area of 300 to 1500
m.sup.2/g and ii) a porosity of 50% or more, a multivalent metal
salt, an organic acid and a polyhydric alcohol.
[0010] In another aspect of the present invention, there is
provided a method for preparing an attrition-resistant
superabsorbent polymer comprising:
[0011] adding water; and
[0012] at least three selected from the group consisting of
particles having the above features i) and ii), a multivalent metal
salt, an organic acid and a polyhydric alcohol to a superabsorbent
polymer, thus preparing a hydrous superabsorbent polymer.
[0013] In still another aspect of the present invention, there is
provided a composition for preparing an attrition-resistant
superabsorbent polymer comprising water; and at least three
selected from the group consisting of particles having the features
i) and ii), a multivalent metal salt, an organic acid and a
polyhydric alcohol.
Advantageous Effects
[0014] According to the present invention, it has an effect of
providing a superabsorbent polymer in which attrition resistance is
improved and the improved attrition resistance is maintained for a
long time, while having physical properties superior or equal to a
conventional superabsorbent polymer.
DESCRIPTION OF DRAWINGS
[0015] FIG. 1 shows the experimental results of Experimental
Example 1 of the present invention.
BEST MODE
[0016] Hereinafter, the present invention will be described in more
detail.
[0017] The present invention relates to an attrition-resistant
superabsorbent polymer comprising:
[0018] a superabsorbent polymer;
[0019] water; and
[0020] at least three selected from the group consisting of
particles having i) a BET specific surface area of 300 to 1500
m.sup.2/g and ii) a porosity of 50% or more, a multivalent metal
salt, an organic acid and a polyhydric alcohol.
[0021] In one embodiment of the present invention, the particles
may be preferably contained in an amount of 0.0001 to 15 parts by
weight based on 100 parts by weight of the superabsorbent polymer,
more preferably 0.001 to 2.0 parts by weight, and most preferably
0.05 to 0.15 parts by weight based on 100 parts by weight of the
superabsorbent polymer.
[0022] When the content of the particles is less than the
aforementioned range, it may not be sufficient to obtain the
expected effect, and when the content exceeds the above range, the
particles are used in an excessive amount, which is not
economically preferred.
[0023] Typically, a superabsorbent polymer has a hydrophilic
surface, and because of capillary force, hydrogen bonding,
polymeric inter-particular diffusion, or intermolecular Van der
Waals force, resulting from water present between particles upon
drying after moisture absorption, an irreversible agglomeration may
occur. Therefore, since water is essentially used even in the
polymerization and surface crosslinking process of the
superabsorbent polymer, an agglomeration may occur and so an
internal load may increase, and ultimately, it may be a cause of
damaging the equipment. Further, since the agglomerated
superabsorbent polymers have a large particle size, which are
unsuitable for practical use, there is disadvantage in that a
deagglomeration process has to be introduced so as to decrease the
particle size to an appropriate size. Also, strong force is applied
during deagglomeration process, and thus, there existed a problem
that the physical properties of the superabsorbent polymers could
be deteriorated due to attrition of the superabsorbent
polymers.
[0024] In order to solve these problems, attempts have been made to
introduce a variety of fine particles, which are present on the
surface of the superabsorbent polymer and can function to prevent
direct agglomeration of the polymer particles. However, when the
fine particles were added in an excessive amount, an aglomeration
could be prevented, but there existed a disadvantage that the
absorbency under pressure of the superabsorbent polymer was
decreased.
[0025] To solve such problems, the particles introduced in the
superabsorbent polymer of the present invention may have a particle
size ranging from 2 nm to 50 .mu.m. Further, the particles may have
a BET specific surface area of 300 to 1500 m.sup.2/g, preferably
500 to 1500 m.sup.2/g, and more preferably 600 to 1500 m.sup.2/g.
Furthermore, the fine particles may have superhydrophobicity with a
water contact angle of 125.degree. or more, preferably 135.degree.
or more, and more preferably 140.degree. or more. In addition, the
particles may have a particle size ranging from 2 nm to 50 .mu.m
and superhydrophobicity with a water contact angle of 125.degree.
or more.
[0026] Moreover, the particles may have a porosity of 50% or more,
and preferably 90% or more. As the attrition-resistant
superabsorbent polymer uses the particles having the aforementioned
features, the effect of water present on the surface of the polymer
may decrease, and further as fine particles having porous
superhydrophobicity are used, the agglomeration may be remarkably
reduced. In addition, even when a relatively small amount of fine
particles is used, permeability may be easily increased, and the
absorbency under pressure may be readily maintained.
[0027] The particles added in the method for preparing a
superabsorbent polymer according to the present invention are not
limited by its components as long as they are substances having the
aforementioned features. Specifically, inorganic oxides, such as
silica (SiO.sub.2), alumina, titania (TiO.sub.2) or carbon,
inorganic compounds, organic polymers, ion exchange resins, metals,
metal salts, and the like may be used, but are not limited
thereto.
[0028] Further, as the process of adding the particles, a method of
dispersing particles in a monomer solution, adding particles to a
hydrogel polymer and then dry mixing them with primarily dried
polymer particles, dispersing particles in water or an organic
solvent in which a surface crosslinking agent is dissolved upon
surface crosslinking, dry mixing particles separately from water or
an organic solvent in which a surface crosslinking agent is
dissolved upon surface crosslinking, or dry mixing particles with a
surface-crosslinked product, etc. may be used, but is not limited
thereto.
[0029] In another embodiment of the present invention, the water in
the attrition-resistant superabsorbent polymer may be preferably
contained in an amount of 1.0 to 20.0 parts by weight, more
preferably 1.0 to 10.0 parts by weight, and most preferably 2.5 to
7.5 parts by weight based on 100 parts by weight of the
superabsorbent polymer and the particles.
[0030] When the content of water is less than the above range, it
may not be sufficient to obtain attrition resistance, and when the
amount exceeds the above range, the surface stickiness of the
polymer may be increased, and irreversible agglomeration between
the superabsorbent polymer particles may occur, resulting in a
decrease in processability of the polymer and changing the particle
size at the same time, and thus, a problem may arise that it may
not be suitably used as a product.
[0031] In the preparation process of a superabsorbent polymer,
water is a polymerization medium, and is used in various
applications, including facilitating the dispersion of the
crosslinking solution during the surface crosslinking process, or
the like. Further, residual moisture in the final product functions
as an anti-static agent and a plasticizer for resin, and plays a
role in suppressing the formation of very small superabsorbent
polymer dust in the application process and preventing the
attrition of the superabsorbent polymer particles. Generally,
however, when water is added even in a small amount to the
superabsorbent polymer, the surface stickiness of the polymer may
be increased by the water absorbed on the surface thereof, and
irreversible agglomeration of the superabsorbent polymer particles
may occur. Such increase in stickiness and agglomeration may result
in a decrease in processability such as a load increase in the
preparation and application processes, consequently increasing the
particle size of the superabsorbent polymer, deteriorating the
physical properties and the productivity. Such superabsorbent
polymers have been studied to date in terms of the polymerization
process thereof and enhancements in absorption capacity thereby,
and surface crosslinking for increasing the surface properties of
the superabsorbent polymer or absorbency under pressure thereof.
Furthermore, research is ongoing into changes in the surface
properties of the superabsorbent polymer in order to solve some
problems, such as to increase permeability or to prevent caking
during storage of the superabsorbent polymer (anti-caking),
etc.
[0032] In the present invention, water is additionally added to the
superabsorbent polymer in the above range to increase the water
content, and the water functions as a plasticizer to minimize the
physical damage of the superabsorbent polymer, thereby
simultaneously satisfying high water content and high
processability. Thus, when water is added to the superabsorbent
polymer, it becomes possible to uniformly contain water without
caking phenomenon. Therefore, when the superabsorbent polymer is
applied to the final products such as diapers, it is advantageous
in that the deterioration of physical properties caused by physical
attrition of the superabsorbent polymer, for example, by
compression or strong air transfer during the production process of
diapers, may be minimized.
[0033] In still another embodiment of the present invention, the
organic acid is preferably contained in an amount of 0.001 to 5.0
parts by weight based on 100 parts by weight of the superabsorbent
polymer, but is not limited thereto.
[0034] When the organic acid is contained in the above range,
attrition resistance of the superabsorbent polymer is enhanced, and
surface hydrophobicity of the superabsorbent polymer caused by
containing the particles defined in the present invention can be
reduced. In addition, it has an advantage in that a decrease in the
absorbency under pressure (AUP) resulting from the use of the
particles defined in the present invention can be minimized.
[0035] When the organic acid is contained in an amount exceeding
the above range, surface stickiness of the superabsorbent polymer
(SAP) occurs, and it may impose a negative influence on the
particle size during post-treatment and thus is not economically
preferable. Further, the anti-caking efficiency is greatly reduced.
In contrast, when the organic acid is contained less than the above
range, the desired effect cannot be achieved.
[0036] The organic acid may be at least one selected from the group
consisting of citric acid, oxalic acid, acetic acid, malic acid,
malonic acid, gluconic acid, ascorbic acid, tartaric acid, succinic
acid, lactic acid, fumaric acid and salicylic acid. Citric acid is
preferred because it is economical, safe and environmentally
friendly, but is not limited thereto.
[0037] In one embodiment of the present invention,
[0038] the polyhydric alcohol may be preferably contained in an
amount of 0.01 to 5.0 parts by weight based on 100 parts by weight
of the superabsorbent polymer, but is not limited thereto.
[0039] When the polyhydric alcohol is used, it is used together
with water, which substantially reduces the amount of water
contained in the superabsorbent polymer, thereby slightly
decreasing the reduction of centrifuge retention capacity (CRC).
Further, it may reduce absorption rate (measured vortex value) and
may help to reduce hydrophobicity. Lastly, it has effects in
increasing attrition resistance of the superabsorbent polymer and
prolonging the retention period thereof.
[0040] When the polyhydric alcohol is contained in an amount
exceeding the above range, a caking phenomenon, in which
superabsorbent polymers are entangled or form an aggregate, may be
induced. In contrast, when the polyhydric alcohol is contained less
than the above range, the desired effect cannot be achieved.
[0041] The polyhydric alcohol may be at least one selected from the
group consisting of propylene glycol, monoethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, monopropylene glycol, 1,3-propanediol,
dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene
glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol and
1,2-cyclohexanedimethanol. Propylene glycol is preferred because it
is economical and safe, but is not limited thereto.
[0042] Further, the present invention relates to a method for
preparing an attrition-resistant superabsorbent polymer
comprising:
[0043] adding water; and at least three selected from the group
consisting of particles having i) a BET specific surface area of
300 to 1500 m.sup.2/g and ii) a porosity of 50% or more, a
multivalent metal salt, an organic acid and a polyhydric alcohol to
a superabsorbent polymer, thus preparing a hydrous superabsorbent
polymer.
[0044] In one embodiment of the present invention, the particles
may be preferably contained in an amount of 0.0001 to 15 parts by
weight based on 100 parts by weight of the superabsorbent polymer,
more preferably 0.001 to 2.0 parts by weight, and most preferably
0.05 to 0.15 parts by weight based on 100 parts by weight of the
superabsorbent polymer.
[0045] When the content of the particles is less than the
aforementioned range, it may not be sufficient to obtain the
expected effect, and when the content exceeds the above range, the
particles are used in an excessive amount, and thus it is not
economically preferred.
[0046] Typically, a superabsorbent polymer has a hydrophilic
surface, and because of capillary force, hydrogen bonding,
polymeric inter-particular diffusion, or intermolecular Van der
Waals force, resulting from water present between the particles
upon drying after moisture absorption, an irreversible
agglomeration may occur. Therefore, since water is essentially used
even in the polymerization and surface crosslinking process of the
superabsorbent polymers, an agglomeration may occur and so an
internal load may increase, and ultimately, it may be a cause of
damaging the equipment. Further, since the agglomerated
superabsorbent polymers have a large particle size, which are
unsuitable for practical use, there is disadvantage in that a
deagglomeration process has to be introduced so as to decrease the
particle size to an appropriate size. Also, strong force is applied
during the deagglomeration process, and thus, there existed a
problem that the physical properties of the superabsorbent polymers
could be deteriorated due to attrition of the superabsorbent
polymers.
[0047] In order to solve these problems, attempts have been made to
introduce a variety of fine particles, which are present on the
surface of the superabsorbent polymer and can function to prevent
direct agglomeration of the polymer particles. In the case where
the fine particles were added in an excessive amount, agglomeration
could be prevented, but there existed a disadvantage that the
absorbency under pressure of the superabsorbent polymer was
decreased.
[0048] To solve such problems, the particles introduced in the
superabsorbent polymer of the present invention may have a particle
size ranging from 2 nm to 50 .mu.m. Further, the particles may have
a BET specific surface area of 300 to 1500 m.sup.2/g, preferably
500 to 1500 m.sup.2/g, and more preferably 600 to 1500 m.sup.2/g.
Furthermore, the fine particles may have superhydrophobicity with a
water contact angle of 125.degree. or more, preferably 135.degree.
or more, and more preferably 140.degree. or more. In addition, the
particles may have a particle size ranging from 2 nm to 50 .mu.m
and superhydrophobicity with a water contact angle of 125.degree.
or more.
[0049] Moreover, the particles may have a porosity of 50% or more,
and preferably 90% or more. As the attrition-resistant
superabsorbent polymer uses the particles having the aforementioned
features, the effect of water present on the surface of the polymer
may decrease, and further as fine particles having porous
superhydrophobicity are used, the agglomeration may be remarkably
reduced. In addition, even when a relatively small amount of fine
particles is used, permeability may be easily increased, and the
absorbency under pressure may be readily maintained.
[0050] The particles added in the method for preparing a
superabsorbent polymer according to the present invention are not
limited by its components as long as they are substances having the
aforementioned features. Specifically, inorganic oxides, such as
silica (SiO.sub.2), alumina, titania (TiO.sub.2) or carbon,
inorganic compounds, organic polymers, ion exchange resins, metals,
metal salts, and the like may be used, but are not limited
thereto.
[0051] Further, as the process of adding the particles, a method of
dispersing particles in a monomer solution, adding particles to a
hydrogel polymer and then dry mixing them with primarily dried
polymer particles, dispersing particles in water or an organic
solvent in which a surface crosslinking agent is dissolved upon
surface crosslinking, dry mixing particles separately from water or
an organic solvent in which a surface crosslinking agent is
dissolved upon surface crosslinking, or dry mixing particles with a
surface-crosslinked product, etc. may be used, but is not limited
thereto.
[0052] In another embodiment of the present invention, the water in
the attrition-resistant superabsorbent polymer may be preferably
contained in an amount of 0.1 to 20.0 parts by weight, more
preferably 1.0 to 10.0 parts by weight, and most preferably 2.5 to
7.5 parts by weight based on 100 parts by weight of the
superabsorbent polymer and the particles.
[0053] When the content of water is less than the above range, it
may not be sufficient to obtain attrition resistance, and when the
amount exceeds the above range, the surface stickiness of the
polymer may be increased, and irreversible agglomeration between
the superabsorbent polymer particles may occur, resulting in a
decrease in processability of the polymer and changing the particle
size at the same time, and thus, a problem may arise that it may
not be suitably used as a product.
[0054] In the preparation process of a superabsorbent polymer,
water is a polymerization medium, and is used in various
applications, including facilitating the dispersion of the
crosslinking solution during the surface crosslinking process, or
the like. Further, residual moisture in the final product functions
as an anti-static agent and a plasticizer for resin, and plays a
role in suppressing the formation of very small superabsorbent
polymer dust in the application process and preventing attrition of
the superabsorbent polymer particles. Generally, however, when
water is added even in a small amount to the superabsorbent
polymer, the surface stickiness of the polymer may be increased by
the water absorbed on the surface thereof, and irreversible
agglomeration of the superabsorbent polymer particles may occur.
Such increase in stickiness and agglomeration may result in a
decrease in processability such as a load increase in the
preparation and application processes, consequently increasing the
particle size of the superabsorbent polymer, deteriorating the
physical properties and the productivity. Such superabsorbent
polymers have been studied to date in terms of the polymerization
process thereof and enhancements in absorption capacity thereby,
and surface crosslinking for increasing the surface properties and
absorbency under pressure of the superabsorbent polymer.
Furthermore, research is ongoing into changes in the surface
properties of the superabsorbent polymer in order to solve some
problems, such as to increase permeability or to prevent caking
during storage of the superabsorbent polymer (anti-caking),
etc.
[0055] In the present invention, water is additionally added to the
superabsorbent polymer in the above range to increase the water
content, and the water functions as a plasticizer to minimize the
physical damage of the superabsorbent polymer, thereby
simultaneously satisfying high water content and high
processability. Thus, when water is added to the superabsorbent
polymer, it becomes possible to uniformly contain water without
caking phenomenon. Therefore, when the superabsorbent polymer is
applied to the final products such as diapers, it is advantageous
in that the deterioration of physical properties caused by physical
attrition of the superabsorbent polymer, for example, by
compression or strong air transfer during the production process of
diapers, may be minimized.
[0056] In still another embodiment of the present invention,
[0057] the organic acid is preferably contained in an amount of
0.001 to 5.0 parts by weight based on 100 parts by weight of the
superabsorbent polymer, but is not limited thereto.
[0058] When the organic acid is contained in the above range,
attrition resistance of the superabsorbent polymer is enhanced, and
surface hydrophobicity of the superabsorbent polymer caused by
containing the particles defined in the present invention can be
reduced. In addition, it has an advantage in that the decrease in
the absorbency under pressure (AUP) resulting from the use of the
particles defined in the present invention can be minimized.
[0059] When the organic acid is contained in an amount exceeding
the above range, surface stickiness of the superabsorbent polymer
(SAP) occurs, and it may impose a negative influence on the
particle size during post-treatment and thus is not economically
preferable. Further, the anti-caking efficiency is greatly reduced.
In contrast, when the organic acid is contained less than the above
range, the desired effect cannot be achieved.
[0060] The organic acid may be at least one selected from the group
consisting of citric acid, oxalic acid, acetic acid, malic acid,
malonic acid, gluconic acid, ascorbic acid, tartaric acid, succinic
acid, lactic acid, fumaric acid and salicylic acid. Citric acid is
preferred because it is economical, safe and environmentally
friendly, but is not limited thereto.
[0061] In one embodiment of the present invention,
[0062] the polyhydric alcohol may be preferably contained in an
amount of 0.01 to 5.0 parts by weight based on 100 parts by weight
of the superabsorbent polymer, but is not limited thereto.
[0063] When the polyhydric alcohol is used, it is used together
with water, which substantially reduces the amount of water
contained in the superabsorbent polymer, thereby slightly
decreasing the reduction of centrifuge retention capacity (CRC).
Further, it may reduce absorption rate (measured vortex value) and
may help to reduce hydrophobicity. Lastly, it has effects in
increasing attrition resistance of the superabsorbent polymer and
prolonging the retention period thereof.
[0064] When the polyhydric alcohol is contained in an amount
exceeding the above range, a caking phenomenon, in which
superabsorbent polymers are entangled or form an aggregate, may be
induced. In contrast, when the polyhydric alcohol is contained less
than the above range, the desired effect cannot be achieved.
[0065] The polyhydric alcohol may be at least one selected from the
group consisting of propylene glycol, monoethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, monopropylene glycol, 1,3-propanediol,
dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene
glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol and
1,2-cyclohexanedimethanol. Propylene glycol is preferred because it
is economical and safe, but is not limited thereto.
[0066] In one embodiment of the present invention, the
superabsorbent polymer is prepared by a method comprising:
[0067] a) carrying out a thermal polymerization or a
photopolymerization of a monomer composition including a
water-soluble ethylenically unsaturated monomer and a
polymerization initiator to prepare a hydrogel polymer;
[0068] b) drying the hydrogel polymer;
[0069] c) milling the dried hydrogel polymer to obtain super
absorbent polymer particles;
[0070] d) adding a surface crosslinking agent to the superabsorbent
polymer particles to carry out a surface crosslinking reaction.
[0071] For reference, as used herein, the term "superabsorbent
polymer particles" refers to particles obtained by drying and
milling the hydrogel polymer. More specifically, the hydrogel
polymer is a material in a hard jelly form with a size of 1 cm or
more and containing water in a large amount (50% or more) after
completion of the polymerization. The superabsorbent polymer
particles are obtained by drying and milling the hydrogel polymer
in a powder form. Thus, the hydrogel polymer corresponds to an
intermediate state of the process.
[0072] First, the superabsorbent polymer used herein undergoes a
step of carrying a thermal polymerization or a photopolymerization
of a monomer composition including a water-soluble ethylenically
unsaturated monomer and a polymerization initiator to prepare a
hydrogel polymer.
[0073] To prepare the superabsorbent polymer of the present
invention, a polymer may be prepared by steps and methods typically
used in the art. Specifically, in the preparation of a
superabsorbent polymer of the present invention, the monomer
composition includes a polymerization initiator. Depending on the
polymerization method, when photopolymerization is carried out, a
photopolymerization initiator is used, and when thermal
polymerization is carried out, a thermal polymerization initiator
is used. However, even when photopolymerization is carried out, a
predetermined amount of heat is generated due to irradiation such
as UV irradiation, and also some heat is generated through the
polymerization reaction, which is an exothermic reaction, and thus
a thermal polymerization initiator may be additionally
included.
[0074] The thermal polymerization initiator used in the preparation
method of the superabsorbent polymer according to the present
invention is not particularly limited, but preferably includes at
least one selected from the group consisting of a persulfate-based
initiator, an azo-based initiator, hydrogen peroxide and ascorbic
acid. Specifically, examples of the persulfate-based initiator may
include sodium persulfate (Na.sub.2S.sub.2O.sub.8), potassium
persulfate (K.sub.2S.sub.2O.sub.8), ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8) and the like, and examples of the
azo-based initiator may include 2,2-azobis(2-amidinopropane)
dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine
dihydrochloride, 2-(carbamoylazo)isobutylonitrile,
2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride,
4,4-azobis-(4-cyanovaleric acid) and the like.
[0075] Further, the photopolymerization initiator used in the
preparation method of the superabsorbent polymer according to the
present invention is not particularly limited, but preferably
includes at least one selected from the group consisting of benzoin
ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl
glyoxylate, benzyl dimethyl ketal, acyl phosphine and
a-aminoketone. Meanwhile, specific examples of the acyl phosphine
may include commercially available lucirin TPO, that is,
2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide.
[0076] Furthermore, in the method for preparing a superabsorbent
polymer according to the present invention, the water-soluble
ethylenically unsaturated monomer is not particularly limited so
long as it is a monomer typically used in the preparation of a
superabsorbent polymer, and preferably includes at least one
selected from the group consisting of an anionic monomer and a salt
thereof, a nonionic hydrophilic monomer, and an amino
group-containing unsaturated monomer and a quaternary salt thereof.
Specifically, at least one selected from the group consisting of
anionic monomers and salts thereof such as acrylic acid,
methacrylic acid, maleic anhydride, fumaric acid, crotonic acid,
itaconic acid, 2-acryloylethanesulfonic acid,
2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic
acid or 2-(meth)acrylamide-2-methylpropane sulfonic acid; non-ionic
hydrophilic monomers such as (meth)acrylamide, N-substituted
(meth)acrylate, 2-hydroxyethyl(meth)acrylate,
2-hydroxypropyl(meth)acrylate, methoxypolyethyleneglycol
(meth)acrylate or polyethyleneglycol (meth)acrylate; and amino
group-containing unsaturated monomers and quaternary salts thereof
such as (N,N)-dimethylaminoethyl (meth)acrylate and
(N,N)-dimethylaminopropyl (meth)acrylamide may be preferably used.
More preferably, acrylic acid or salts thereof may be used. When
acrylic acid or salts thereof are used as the monomer, there is an
advantage in that a superabsorbent polymer having improved
absorbency may be obtained.
[0077] In addition, in the method for preparing a superabsorbent
polymer according to the present invention, in order to impart an
effect in accordance with recycling of resources, fine powder in
the prepared superabsorbent polymer powder, that is, a polymer or
resin powder having a particle size of less than 150 .mu.m may be
incorporated in a predetermined amount in the monomer composition.
Specifically, a polymer or resin powder having a particle size of
less than 150 .mu.m may be added before the initiation of the
polymerization of the monomer composition, or in the early, middle
or late stages after the initiation of polymerization. At this
time, the amount thereof that can be added is not limited, but is
preferably added in an amount of 1 to 10 parts by weight based on
100 parts by weight of the monomer contained in the monomer
composition in order to prevent the deterioration of physical
properties of the finally prepared superabsorbent polymer.
[0078] Meanwhile, in the method for preparing a superabsorbent
polymer according to the present invention, the concentration of
the water-soluble ethylenically unsaturated monomer in the monomer
composition may be appropriately determined and used in
consideration of the polymerization time and the reaction
conditions, and it may preferably be 40 to 55% by weight. When the
concentration of the water-soluble ethylenically unsaturated
monomer is less than 40% by weight, it may be disadvantageous in
view of economy. When the concentration thereof exceeds 55% by
weight, the milling efficiency of the polymerized hydrogel polymer
during milling may decrease.
[0079] The method for preparing hydrogel by carrying out a thermal
polymerization or a photopolymerization of the monomer composition
as described above is not limited by its constitution so long as it
is a polymerization method typically used in the art. Specifically,
polymerization methods are largely classified into thermal
polymerization and photopolymerization, depending on the
polymerization energy source. Typically, the thermal polymerization
may be carried out using a reactor having a stirring spindle, such
as a kneader, and the photopolymerization may be carried out using
a reactor equipped with a movable conveyor belt. However, the
polymerization methods described above are merely illustrative, and
the present invention is not limited to these polymerization
methods.
[0080] For example, as described above, a hydrogel polymer obtained
by providing hot air to a reactor like a kneader equipped with the
agitating spindles, or heating the reactor, and carrying out a
thermal polymerization, which is then discharged through the outlet
of the reactor, may have a size ranging from several cm to several
mm, depending on the type of agitating spindles equipped in the
reactor. Specifically, the size of the hydrogel polymer may vary
depending on the concentration of the monomer mixture to be
injected thereto, the injection speed, or the like, and the
hydrogel polymer having an average particle diameter of about 2 to
50 mm may be generally obtained.
[0081] In addition, as described above, when photopolymerization is
carried out using a reactor equipped with a movable conveyor belt,
a typically obtained hydrogel polymer may be a hydrogel polymer in
the form of a sheet having a width of the belt. At this time, the
thickness of the polymer sheet may vary depending on the
concentration of the monomer composition to be injected thereto,
and the injection speed thereof, but the monomer composition is
preferably provided so as to obtain a typical polymer sheet having
a thickness of 0.5 to 5 cm. In the case where the monomer
composition is provided to an extent that the thickness of the
sheet polymer is too thin, it is not preferable due to low
production efficiency. In contrast, when the thickness of the
polymer sheet is greater than 5 cm, the polymerization reaction may
not be uniformly carried out throughout the entire thickness, due
to excessively thick thickness.
[0082] The light source which can be used in the
photopolymerization step is not particularly limited, and any UV
light source may be used without particular limitation so long as
it is known to trigger a photopolymerization reaction. For example,
a light having a wavelength of about 200 to 400 nm may be used, and
a UV light source such as a Xe lamp, a mercury lamp or a metal
halide lamp may be used. Further, the photopolymerization step may
be carried out at an intensity ranging from about 0.1 mw/cm.sup.2
to about 1 kw/cm.sup.2 for about 5 seconds to about 10 minutes.
When the intensity of light applied to the photopolymerization
reaction and the time thereof are excessively small and short,
sufficient polymerization may not occur. In contrast, when they are
excessively large and long, the quality of the superabsorbent
polymer may be deteriorated.
[0083] Subsequently, in step b), a step of drying the hydrogel
polymer is performed.
[0084] The hydrogel polymer obtained in step a) typically has a
water content of 30 to 60% by weight. As used herein, the term
"water content" refers to a value obtained by subtracting the
weight of polymer in a dried state from the weight of hydrogel
polymer as water content occupied, based on the total weight of the
hydrogel polymer. (Specifically, it is defined as a value
calculated by measuring weight loss of the polymer due to the
evaporation of moisture while drying the polymer by raising the
temperature of the polymer via IR heating. At this time, the drying
is performed in such a manner that the temperature is raised from
room temperature to 180.degree. C. and then maintained at
180.degree. C., and the total drying time is set to 20 minutes,
including 5 minutes of raising the temperature, thereby measuring
the water content.)
[0085] The hydrogel polymer obtained in step a) undergoes a drying
step, and the drying temperature of the drying step may be
150.degree. C. to 250.degree. C. As used herein, the term "drying
temperature" may be defined as the temperature of a heat medium
supplied for the drying process, or the temperature of a drying
reactor containing a heat medium and a polymer in the drying
process.
[0086] When the drying temperature is less than 150.degree. C., the
drying time may become excessively long, and the physical
properties of the finally formed superabsorbent polymer may be
deteriorated. In contrast, when the drying temperature is higher
than 250.degree. C., only the surface of the polymer may be
excessively dried, and thus fine powder may be formed in the
subsequent milling process, and the physical properties of the
finally formed superabsorbent polymer may be deteriorated. The
drying is preferably carried out at a temperature of 150.degree. C.
to 250.degree. C., and more preferably at 160.degree. C. to
200.degree. C.
[0087] Meanwhile, the drying time is not limited, but the drying
may be carried out for 20 to 90 minutes, in consideration of
processing efficiency or the like.
[0088] Further, the drying process of the drying step can also be
used without limitation in its constitution, so long as it is
typically used as a drying process of hydrogel polymers.
Specifically, the drying step may be performed by hot air supply,
IR irradiation, microwave irradiation or UV irradiation, etc. The
polymer after the drying process may have a water content of 0.1 to
10% by weight.
[0089] Meanwhile, the method for preparing the superabsorbent
polymer according to the present invention may further include
simple milling step before the drying step, as needed, in order to
increase efficiency of the drying step. The simple milling step
before the drying step is carried out so that the particle size of
the hydrogel polymer falls in the range of 1 to 15 mm. To mill the
polymer to have a particle size of less than 1 mm is technically
difficult due to the high water content of the hydrogel polymer,
and the milled particles may agglomerate together. In contrast,
when the polymer is milled to have a particle size larger than 15
mm, the effect of increasing the efficiency of the subsequent
drying step by the milling process may be insignificant.
[0090] In the simple milling step before the drying step, the
milling device used is not limited in its constitution.
Specifically, examples thereof may include any one milling device
selected from the group consisting of a vertical pulverizer, a
turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill,
a disc mill, a shred crusher, a crusher, a chopper, and a disc
cutter, but the mill is not limited to the examples described
above.
[0091] When the milling step is performed to increase the drying
efficiency before the drying step, the polymer, which has high
water content, may adhere to the surface of the mill. Thus, in
order to increase the efficiency of the milling step before drying
the hydrogel polymer, an additive or the like capable of preventing
adhering upon milling may be further used. Specifically, the type
of additives that can be used is not limited in its constitution,
and examples thereof may include a fine powder agglomeration
inhibitor, such as steam, water, a surfactant, and inorganic
powder, such as clay or silica; a thermal polymerization initiator,
such as a persulfate-based initiator, an azo-based initiator,
hydrogen peroxide, and ascorbic acid; and a crosslinking agent,
such as an epoxy-based crosslinking agent, a diol-based
crosslinking agent, a crosslinking agent containing a bifunctional
or trifunctional or higher polyfunctional acrylate, and a
monofunctional compound having a hydroxyl group, but the additives
are not limited to the examples described above.
[0092] After the drying step, the method for preparing the
superabsorbent polymer according to the present invention undergoes
step c) of milling the dried hydrogel polymer to obtain
superabsorbent polymer particles. The superabsorbent polymer
particles obtained after the milling step may have a particle size
of 150 to 850 .mu.m. In the method for preparing a superabsorbent
polymer according to the present invention, the milling device used
for milling the particles to have the particle size may
specifically include a pin mill, a hammer mill, a screw mill, a
roll mill, a disc mill, or a jog mill, but is not limited
thereto.
[0093] Subsequently, in step d), a surface crosslinking agent is
added to the superabsorbent polymer particles to carry out surface
crosslinking reaction. In step above, the surface crosslinking
agent is added, and the composition of the surface crosslinking
agent added to each of the superabsorbent polymer particles may be
the same, or a different composition may be added as needed,
depending on the particle size thereof.
[0094] The surface crosslinking agent added in the method for
preparing a superabsorbent polymer according to the present
invention is not limited in its constitution, so long as it is able
to react with a functional group of the polymer. In order to
improve the properties of the produced superabsorbent polymer, the
surface crosslinking agent may preferably include at least one
selected from the group consisting of a polyhydric alcohol
compound; an epoxy compound; a polyamine compound; a haloepoxy
compound; a condensation product of haloepoxy compound; an
oxazoline compound; a mono-, di- or poly oxazolidinone compound; a
cyclic urea compound; a multivalent metal salt; and an alkylene
carbonate compound.
[0095] Specifically, examples of the polyhydric alcohol compound
may include at least one selected from the group consisting of
mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene
glycol, 1,3-propanediol, dipropylene glycol,
2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol,
polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol,
1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol.
[0096] Further, examples of the epoxy compound may include ethylene
glycol diglycidyl ether and glycidol, etc., and examples of the
polyamine compound may include at least one selected from the group
consisting of ethylene diamine, diethylene triamine, triethylene
tetramine, tetraethylene pentamine, pentaethylene hexamine,
polyethyleneimine, and polyamidepolyamine.
[0097] Furthermore, examples of the haloepoxy compound may include
epichlorohydrin, epibromohydrin and .alpha.-methyl epichlorohydrin.
Meanwhile, examples of the mono-, di- or polyoxazolidinone compound
may include 2-oxazolidinone or the like.
[0098] In addition, examples of the alkylene carbonate compound may
include ethylene carbonate or the like. These compounds may be used
alone or in combination. Meanwhile, in order to increase the
efficiency of the surface crosslinking process, among these surface
crosslinking agents, the surface crosslinking agents may be
preferably used by containing at least one polyhydric alcohol
compound, and more preferably, a polyhydric alcohol compound having
2 to 10 carbon atoms may be used.
[0099] In addition, the amount of the surface crosslinking agent
added for the surface treatment of the polymer particles by mixing
the surface crosslinking agent as described above may be
appropriately determined depending on the type of the surface
crosslinking agent specifically added or the reaction conditions,
and it may be used in an amount of 0.001 to 5 parts by weight,
preferably 0.01 to 3 parts by weight, and more preferably 0.05 to 2
parts by weight, based on 100 parts by weight of the typical milled
superabsorbent polymer particles.
[0100] When the amount of the surface crosslinking agent is too
small, the surface crosslinking reaction does not readily occur. In
contrast, when the amount thereof exceeds 5 parts by weight based
on 100 parts by weight of the polymer, the physical properties of
the superabsorbent polymer may rather deteriorate due to excessive
surface crosslinking reactions.
[0101] At this time, the method of adding the surface crosslinking
agent to the polymer is not limited in its constitution. Methods
such as adding and mixing the surface crosslinking agent and the
polymer powder in a reaction bath, spraying the surface
crosslinking agent onto the polymer powder, or mixing by
continuously supplying the polymer and the crosslinking agent in a
reaction bath, such as a mixer, which operates continuously, may be
used.
[0102] Further, the surface temperature of the polymer in the step
of adding the surface crosslinking agent is preferably 60.degree.
C. to 90.degree. C.
[0103] Furthermore, according to one embodiment of the present
invention, the temperature of the polymer itself may be preferably
20.degree. C. to 80.degree. C. when adding the surface crosslinking
agent, in order to raise the temperature to the reaction
temperature for the surface crosslinking reaction within 1 to 60
minutes after adding the surface crosslinking agent. In order to
realize the above temperature of the polymer, a process that is
carried out after the drying step, which is carried out at a
relatively high temperature, is continuously performed, and the
processing time may be shortened. Alternatively, the polymer may be
heated separately when it is difficult to shorten the processing
time.
[0104] In addition, in the method for preparing a superabsorbent
polymer according to the present invention, the surface
crosslinking agent itself added to the polymer may be heated so as
to raise the temperature to the reaction temperature for the
surface crosslinking reaction within 1 to 60 minutes after adding
the surface crosslinking agent.
[0105] Meanwhile, the method for preparing a superabsorbent polymer
according to the present invention is capable of improving
efficiency of the surface crosslinking process when carrying out
the surface crosslinking reaction after raising the temperature to
the reaction temperature for the surface crosslinking reaction
within 1 minute to 60 minutes. Consequently, a superabsorbent
polymer having excellent physical properties may be obtained while
minimizing the content of residual monomer of the finally obtained
superabsorbent polymer. Herein, the temperature of the added
surface crosslinking agent may be adjusted to 5.degree. C. to
60.degree. C., and more preferably to 10.degree. C. to 40.degree.
C. When the temperature of the surface crosslinking agent is lower
than 5.degree. C., the effect of reducing the rate of raising a
temperature to the temperature of the surface crosslinking reaction
obtained by raising the temperature of the surface crosslinking
agent is insignificant. In contrast, when the temperature of the
surface crosslinking agent is higher than 60.degree. C., the
surface crosslinking agent may not be uniformly dispersed in the
polymer. As used herein, the surface crosslinking reaction
temperature may be defined as the combined temperature of the
polymer and the surface crosslinking agent that is added for the
crosslinking reaction.
[0106] Further, the means for raising the temperature for the
surface crosslinking reaction is not limited in its constitution.
Specifically, a heating medium may be supplied, or direct heating
may be used by means of electricity or the like, however, the
present invention is not limited to the examples described above.
Specific examples of a heat source that can be used may include
steam, electricity, UV rays, IR rays and the like, and in addition,
a heated thermal fluid or the like may be used.
[0107] Meanwhile, in the method of preparing a superabsorbent
polymer according to the present invention, the crosslinking
reaction may be carried out for 1 to 60 minutes, preferably 5 to 40
minutes, and most preferably 10 to 20 minutes after raising the
temperature for the crosslinking reaction. When the crosslinking
reaction time is less than 1 minute, which is excessively short,
sufficient crosslinking reaction may not occur. In contrast, when
the crosslinking reaction time is longer than 60 minutes, the
physical properties of the superabsorbent polymer may rather
deteriorate due to the excessive surface crosslinking reaction, and
attrition of the polymer may occur due to long-term retention in
the reactor.
[0108] In addition, the present invention relates to a composition
for preparing an attrition-resistant superabsorbent polymer
comprising:
[0109] water; and
[0110] at least three selected from the group consisting of
particles having i) a BET specific surface area of 300 to 1500
m.sup.2/g and ii) a porosity of 50% or more, a multivalent metal
salt, an organic acid and a polyhydric alcohol.
[0111] In one embodiment of the present invention, the particles
may be preferably contained in an amount of 0.0001 to 15 parts by
weight based on 100 parts by weight of the superabsorbent polymer,
more preferably 0.001 to 2.0 parts by weight, and most preferably
0.05 to 0.15 parts by weight based on 100 parts by weight of the
superabsorbent polymer.
[0112] When the content of the particles is less than the
aforementioned range, it may not be sufficient to obtain the
expected effect, and when the content exceeds the above range, the
particles are used in an excessive amount, and thus it is not
economically preferred.
[0113] Typically, a superabsorbent polymer has a hydrophilic
surface, and because of capillary force, hydrogen bonding,
polymeric inter-particular diffusion, or intermolecular Van der
Waals force, resulting from water present between the particles
upon drying after moisture absorption, an irreversible
agglomeration may occur Therefore, since water is essentially used
even in the polymerization and surface crosslinking process of the
superabsorbent polymers, an agglomeration may occur and so an
internal load may increase, and ultimately, it may be a cause of
damaging the equipment. Further, since the agglomerated
superabsorbent polymers have a large particle size, which are
unsuitable for practical use, there is disadvantage in that a
deagglomeration process has to be introduced so as to decrease the
particle size to an appropriate size. Also, strong force is applied
during the deagglomeration process, and thus, there existed a
problem that the physical properties of the superabsorbent polymers
could be deteriorated due to attrition of the superabsorbent
polymers.
[0114] In order to solve these problems, attempts have been made to
introduce a variety of fine particles, which are present on the
surface of the superabsorbent polymer and can function to prevent
direct agglomeration of the polymer particles. In the case where
the fine particles were added in an excessive amount, agglomeration
could be prevented, but there existed a disadvantage that the
absorbency under pressure of the superabsorbent polymer was
decreased.
[0115] To solve such problems, the particles introduced in the
superabsorbent polymer of the present invention may have a particle
size ranging from 2 nm to 50 .mu.m. Further, the particles may have
a BET specific surface area of 300 to 1500 m.sup.2/g, preferably
500 to 1500 m.sup.2/g, and more preferably 600 to 1500 m.sup.2/g.
Furthermore, the fine particles may have superhydrophobicity with a
water contact angle of 125.degree. or more, preferably 135.degree.
or more, and more preferably 140.degree. or more. In addition, the
particles may have a particle size ranging from 2 nm to 50 .mu.m
and superhydrophobicity with a water contact angle of 125.degree.
or more.
[0116] Moreover, the particles may have a porosity of 50% or more,
and preferably 90% or more. As the attrition-resistant
superabsorbent polymer uses the particles having the aforementioned
features, it can reduce the effect of water present on the surface
of the polymer, and further as fine particles having porous
superhydrophobicity are used, the agglomeration may be remarkably
reduced. In addition, even when a relatively small amount of fine
particles is used, permeability may be easily increased, and the
absorbency under pressure may be readily maintained.
[0117] The particles added in the method for preparing a
superabsorbent polymer according to the present invention are not
limited by its components as long as they are substances having the
aforementioned features. Specifically, inorganic oxides, such as
silica (SiO.sub.2), alumina, titania (TiO.sub.2) or carbon,
inorganic compounds, organic polymers, ion exchange resins, metals,
metal salts, and the like may be used, but are not limited
thereto.
[0118] Further, as the process of adding the particles, a method of
dispersing particles in a monomer solution, adding particles to a
hydrogel polymer and then dry mixing them with primarily dried
polymer particles, dispersing particles in water or an organic
solvent in which a surface crosslinking agent is dissolved upon
surface crosslinking, dry mixing particles separately from water or
an organic solvent in which a surface crosslinking agent is
dissolved upon surface crosslinking, or dry mixing particles with a
surface-crosslinked product, etc. may be used, but is not limited
thereto.
[0119] In another embodiment of the present invention, the water in
the attrition-resistant superabsorbent polymer may be preferably
contained in an amount of 0.1 to 20.0 parts by weight, more
preferably 1.0 to 10.0 parts by weight, and most preferably 2.5 to
7.5 parts by weight based on 100 parts by weight of the
superabsorbent polymer and the particles.
[0120] When the content of water is less than the above range, it
may not be sufficient to obtain attrition resistance, and when the
amount exceeds the above range, the surface stickiness of the
polymer may be increased, and irreversible agglomeration between
the superabsorbent polymer particles may occur, resulting in a
decrease in processability of the polymer and changing the particle
size at the same time, and thus, a problem may arise that it may
not be suitably used as a product.
[0121] In the preparation process of a superabsorbent polymer,
water is a polymerization medium, and is used in various
applications, including facilitating the dispersion of the
crosslinking solution during the surface crosslinking process, or
the like. Further, residual moisture in the final product functions
as an anti-static agent and a plasticizer for resin, and plays a
role in suppressing the formation of very small superabsorbent
polymer dust in the application process and preventing milling of
the superabsorbent polymer particles. Generally, however, when
water is added even in a small amount to the superabsorbent
polymer, the surface stickiness of the polymer may be increased by
the water absorbed on the surface thereof, and irreversible
agglomeration of the superabsorbent polymer particles may occur.
Such increase in stickiness and agglomeration may result in a
decrease in processability such as a load increase in the
preparation and application processes, consequently increasing the
particle size of the superabsorbent polymer, deteriorating the
physical properties thereof and decreasing productivity. Such
superabsorbent polymers have been studied to date in terms of the
polymerization process thereof and enhancements in absorption
capacity thereby, and surface crosslinking for increasing the
surface properties of the superabsorbent polymer or absorbency
under pressure thereof. Furthermore, research is ongoing into
changes in the surface properties of the superabsorbent polymer in
order to solve some problems, such as to increase permeability or
to prevent caking during storage of the superabsorbent polymer
(anti-caking), etc.
[0122] In the present invention, water is additionally added to the
superabsorbent polymer in the above range to increase the water
content, and the water functions as a plasticizer to minimize the
physical damage of the superabsorbent polymer, thereby
simultaneously satisfying high water content and high
processability, and thus, when water is added to the superabsorbent
polymer, it becomes possible to uniformly contain water without
caking phenomenon. Therefore, when the superabsorbent polymer is
applied to the final products of diapers or the like, it is
advantageous in that the deterioration of physical properties
caused by physical attrition of the superabsorbent polymer, for
example, by compression or strong air transfer during the
production process of diapers, may be minimized.
[0123] In still another embodiment of the present invention,
[0124] the organic acid is preferably contained in an amount of
0.001 to 5.0 parts by weight based on 100 parts by weight of the
superabsorbent polymer, but is not limited thereto.
[0125] When the organic acid is contained in the above range,
attrition resistance of the superabsorbent polymer is enhanced, and
surface hydrophobicity of the superabsorbent polymer caused by
containing the particles defined in the present invention can be
reduced. In addition, it has an advantage in that a decrease in the
absorbency under pressure (AUP) resulting from the use of the
particles defined in the present invention can be minimized.
[0126] When the organic acid is contained in an amount exceeding
the above range, surface stickiness of the superabsorbent polymer
(SAP) occurs, and it may impose a negative influence on the
particle size during post-treatment and thus is not economically
preferable. Further, the anti-caking efficiency is greatly reduced.
In contrast, when the organic acid is contained less than the above
range, the desired effect cannot be achieved.
[0127] The organic acid may be at least one selected from the group
consisting of citric acid, oxalic acid, acetic acid, malic acid,
malonic acid, gluconic acid, ascorbic acid, tartaric acid, succinic
acid, lactic acid, fumaric acid and salicylic acid. Citric acid is
preferred because it is economical, safe and environmentally
friendly, but is not limited thereto.
[0128] In one embodiment of the present invention,
[0129] the polyhydric alcohol may be preferably contained in an
amount of 0.01 to 5.0 parts by weight based on 100 parts by weight
of the superabsorbent polymer, but is not limited thereto.
[0130] When the polyhydric alcohol is used, it is used together
with water, which substantially reduces the amount of water
contained in the superabsorbent polymer, thereby slightly
decreasing the reduction of centrifuge retention capacity (CRC).
Further, it may reduce absorption rate (measured vortex value) and
may help to reduce hydrophobicity. Lastly, it has effects in
increasing attrition resistance of the superabsorbent polymer and
prolonging the retention period thereof.
[0131] When the polyhydric alcohol is contained in an amount
exceeding the above range, a caking phenomenon, in which
superabsorbent polymers are entangled or form an aggregate, may be
induced. In contrast, when the polyhydric alcohol is contained less
than the above range, the desired effect cannot be achieved.
[0132] The polyhydric alcohol may be at least one selected from the
group consisting of propylene glycol, monoethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, monopropylene glycol, 1,3-propanediol,
dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene
glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol and
1,2-cyclohexanedimethanol. Propylene glycol is preferred because it
is economical and safe, but is not limited thereto.
Detailed Description of the Embodiments
[0133] Hereinafter, the present invention will be described in more
detail by way of non-limiting Examples. However, the embodiments of
the present invention disclosed below are given for illustrative
purposes only, and the scope of the present invention is not
intended to be limited by these Examples. The scope of the present
invention is given by the accompanying claims, and also contains
all modifications within the meaning and range equivalent to the
claims. Unless otherwise mentioned, "%" and "part", which indicate
the amounts in the following Examples and Comparative Examples, are
given on a mass basis.
EXAMPLES
Preparation Example: Preparation of Hydrogel Polymer
[0134] 100 g of acrylic acid, 0.3 g of polyethylene glycol
diacrylate as a crosslinking agent, 0.033 g of
diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide as an initiator,
38.9 g of sodium hydroxide (NaOH), and 103.9 g of water were mixed
to prepare a monomer mixture.
[0135] Thereafter, the monomer mixture was placed in a continuously
moving conveyor belt and irradiated with UV rays (irradiation
intensity: 2 mW/cm.sup.2) to carry out UV polymerization for 2
minutes, thereby obtaining a hydrogel polymer.
Examples: Preparation of Superabsorbent Polymer
Example 1. Preparation of Superabsorbent Polymer Having Improved
Attrition Resistance
[0136] (1) The hydrogel polymer prepared according to the
Preparation Example was cut into a size of 5*5 mm, dried in a hot
air oven at 170.degree. C. for 2 hours, milled using a pin mill to
obtain a superabsorbent polymer having a particle size of 150 .mu.m
to 850 .mu.m using a sieve.
[0137] (2) 0.025% by weight of Aerogel, namely, porous
superhydrophobic fine particles (manufactured by JIOS), was added
to the superabsorbent polymer based on 100% by weight of the
superabsorbent polymer and stirred. Then, 0.064% by weight of
citric acid and 0.64% by weight of aluminum sulfate were dissolved
in 3.0% by weight of water, and then added to a stirrer.
[0138] Aerogel used had an average particle size of 5 .mu.m, a BET
specific surface area of 720 m.sup.2/g, a water contact angle of
144.degree., and a porosity of 95%.
[0139] The particle sizes of Aerogel were measured and analyzed in
accordance with the ISO 13320 by laser diffraction using a
Helium-Neon Laser Optical System (HELOS). The BET specific surface
area and the porosity were measured using a BET analyzer. The
contact angle for water was measured using a contact angle analyzer
(KRUSS DSA100). Specifically, a double-sided tape was applied onto
a flat glass plate and then fine particles were coated thereon to a
monolayer, and when 5 .mu.l of ultrapure water was placed on the
monolayer, the ultrapure water was placed in a drop form, and the
angle formed between the water drop and the glass plate was
repeatedly measured 4 times and then an average value was
calculated.
Example 2. Preparation of Superabsorbent Polymer Having Improved
Attrition Resistance
[0140] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 1.0% by weight of propylene glycol was
further added in step (2) of Example 1.
Example 3. Preparation of Superabsorbent Polymer Having Improved
Attrition Resistance
[0141] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 0.025% by weight of Aerogel, namely,
porous superhydrophobic fine particles (manufactured by JIOS), was
added to the superabsorbent polymer prepared in step (1) of Example
1 based on 100% by weight of the superabsorbent polymer and
stirred, and 0.64% by weight of aluminum sulfate and 1.0% by weight
of aluminum propylene glycol were dissolved in 3.0% by weight of
water and then added to a stirrer.
Comparative Example 1. Preparation of Superabsorbent Polymer
[0142] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that step (2) of Example 1 was not carried
out.
Comparative Example 2. Preparation of Superabsorbent Polymer
[0143] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 0.025% by weight of Aerogel, namely,
porous superhydrophobic fine particles (manufactured by JIOS), was
added and stirred, and then 4% by weight of water (citric acid and
aluminum sulfate were not added) was added in step (2) of Example
1.
Comparative Example 3. Preparation of Superabsorbent Polymer
[0144] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that citric acid was not added in step (2) of
Example 1.
Reference Examples: Preparation of Superabsorbent Polymer to which
Aerogel and Citric Acid are Added
Reference Example 1. Preparation of Superabsorbent Polymer
[0145] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 0.025% by weight of aerogel, namely,
porous superhydrophobic fine particles (manufactured by JIOS), was
added to the superabsorbent polymer based on 100% by weight of the
superabsorbent polymer and stirred, and 0.064% by weight of citric
acid was dissolved in 3.0% by weight of water and then added to a
stirrer in step (2) of Example 1.
Reference Example 2. Preparation of Superabsorbent Polymer
[0146] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 0.025% by weight of Aerogel, namely,
porous superhydrophobic fine particles (manufactured by JIOS), was
added to the superabsorbent polymer based on 100% by weight of the
superabsorbent polymer and stirred, and 0.160% by weight of citric
acid was dissolved in 4% by weight of water and then added to a
stirrer in step (2) of Example 1.
Reference Example 3. Preparation of Superabsorbent Polymer
[0147] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 0.025% by weight of Aerogel, namely,
porous superhydrophobic fine particles (manufactured by JIOS), was
added to the superabsorbent polymer based on 100% by weight of the
superabsorbent polymer and stirred, and 0.320% by weight of citric
acid was dissolved in 4% by weight of water and then added to a
stirrer in step (2) of Example 1.
Reference Example 4. Preparation of Superabsorbent Polymer
[0148] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that 0.025% by weight of Aerogel, namely,
porous superhydrophobic fine particles (manufactured by JIOS), was
added to the superabsorbent polymer based on 100% by weight of the
superabsorbent polymer and stirred, and 1.0% by weight of propylene
glycol was dissolved in 3.0% by weight of water and then added to a
stirrer in step (2) of Example 1.
Reference Example 5. Preparation of Superabsorbent Polymer
[0149] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that Aerogel, namely, porous superhydrophobic
fine particles (manufactured by JIOS), was not added to the
superabsorbent polymer, and 0.64% by weight of aluminum sulfate was
dissolved in 3.0% by weight of water based on 100% by weight of the
superabsorbent polymer and then added to a stirrer in step (2) of
Example 1.
Reference Example 6. Preparation of Superabsorbent Polymer
[0150] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that Aerogel, namely, porous superhydrophobic
fine particles (manufactured by JIOS), was not added to the
superabsorbent polymer, and 0.064% by weight of citric acid was
dissolved in 1.0% by weight of propylene glycol based on 100% by
weight of the superabsorbent polymer and then added to a stirrer in
step (2) of Example 1.
Reference Example 7. Preparation of Superabsorbent Polymer
[0151] A superabsorbent polymer was prepared in the same manner as
in Example 1, except that Aerogel, namely, porous superhydrophobic
fine particles (manufactured by JIOS), was not added to the
superabsorbent polymer, and 0.064% by weight of citric acid was
dissolved in 3.0% by weight of water based on 100% by weight of the
superabsorbent polymer and then added to a stirrer in step (2) of
Example 1.
EXPERIMENTAL EXAMPLES
Experimental Example 1. Test on the Presence or Absence of
Hydrophobicity and Water Absorption
[0152] The test was carried out in the following manner in order to
simply determine the presence or absence of hydrophobicity of the
superabsorbent polymers and water absorption, and the results are
shown in FIG. 1.
[0153] After immersing 200 mL of deionized water (DI water) into a
600 mL beaker, 2 g of superabsorbent polymer (SAP) was added
simultaneously, and the change pattern was observed immediately
after the addition and after 20 seconds of addition.
[0154] In the case of Comparative Example 2 (#2) and Comparative
Example 3 (#3), the hydrophobic nature of Aerogel caused the
superabsorbent polymers to float without being sank. In the case of
Comparative Example 3 (#3), the addition of aluminum sulfate, which
is a multivalent metal salt, caused the superabsorbent polymer to
sink relatively quickly compared to the test of Comparative Example
2 (#2). In the case of Example 2 (#4), similar to the case of
Comparative Example 1 (#1) in which no treatment was performed, the
absorption behavior in which the superabsorbent polymer gradually
swelled after sinking was exhibited even though it contained the
Aerogel, thereby confirming that the hydrophobicity could be
remarkably improved upon treatment with citric acid and propylene
glycol.
Experimental Example 2-1. Attrition Resistance Test
[0155] The attrition resistance confirmation test was carried out
by ball milling in order to simulate and confirm the degree of
decrease in physical properties when the superabsorbent polymer was
finally applied to a product.
[0156] 10 pieces of alumina balls having a diameter of 2.5 cm and
20 g of the superabsorbent polymers prepared in Example 1 and
Example 2 and Comparative Examples 1 to 3 were added to a jar
having an internal diameter of 10 cm and subjected to ball milling
under the condition of 300 rpm for 20 minutes. The results are
shown as a change in particle size before and after ball milling
(%), and are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Change in particle size before and after
ball milling (%) Example 1 -9.0 Example 2 -5.8 Example 3 -6.4
Comparative -17.5 Example 1 Comparative -10.0 Example 2 Comparative
-10.7 Example 3
[0157] The above results showed that the attrition resistance of
the superabsorbent polymers of Example 2 and Example 3, which
include at least three selected from the group consisting of
Aerogel, citric acid, aluminum sulfate and propylene glycol, was
significantly improved.
Experimental Example 2-2. Attrition Resistance Test
[0158] The attrition resistance test was carried out on the
superabsorbent polymers prepared in Reference Examples 1 to 7, in
which citric acid was added when preparing the superabsorbent
polymers, in the same manner as in Experimental Example 2-1. The
results are shown as a change in particle size before and after
ball milling (%) and a water content (%), and are shown in Table 2
below
TABLE-US-00002 TABLE 2 Change in particle size before and after
ball milling Water content (%) (%) Reference -11.5 4.4 Example 1
Reference -12.8 4.4 Example 2 Reference -11.2 4.4 Example 3
Reference -12.7 5.2 Example 4 Reference -9.3 4.9 Example 5
Reference -20.5 3.0 Example 6 Reference -10.9 4.8 Example 7
Experimental Example 3. Centrifuge Retention Capacity (CRC)
[0159] The centrifuge retention capacity (CRC) was measured for
each of the superabsorbent polymers prepared in Examples 1 to 3,
Comparative Examples 1 to 3 and Reference Examples 1 to 7. The
measurement of the centrifuge retention capacity was carried out in
the following manner. After uniformly adding W.sub.0(g) (about 0.1
g) of each of the superabsorbent polymers in a nonwoven fabric-made
bag and sealing the same, they were immersed in a 0.9 wt %
physiological saline solution at room temperature. After 30
minutes; water was removed from the bag by centrifugation at 250 G
for 3 minutes, and the weight W.sub.2(g) of the bag was then
measured. Meanwhile, the same procedure was carried out without
using the polymers, and then the resultant weight W.sub.1(g) was
measured. Using the respective weights thus obtained, the
centrifuge retention capacity (g/g) was determined according to the
following Equation.
CRC(g/g)={[W.sub.2(g)-(g)]/W.sub.0(g)}-1
[0160] The test results are shown in Table 3 below.
Experimental Example 4. Absorbency Under Pressure (AUP)
[0161] The absorbency under pressure (AUP) was measured for each of
the superabsorbent polymers prepared in Examples 1 to 3,
Comparative Examples 1 to 3 and Reference Examples 1 to 7. The
absorbency under pressure was carried out in the following manner.
A 400 stainless mesh was installed at the bottom of a plastic
cylinder having an inner diameter of 60 mm. 0.90 g of each of the
superabsorbent polymers prepared in Example 1 and Example 2 and
Comparative Examples 1 to 3 were uniformly scattered on the mesh
under conditions of room temperature and relative humidity of 50%.
A piston which can further uniformly provide a load of 4.83 kPa
(0.7 psi) was put thereon. The external diameter of the piston was
slightly smaller than 60 mm, there was no gap between the
cylindrical internal wall and the piston, and the jig-jog of the
cylinder was not interrupted. At this time, the weight W.sub.a(g)
of the device was measured. A glass filter having a diameter of 90
mm and a thickness of 5 mm was placed on a Petri dish having the
diameter of 150 mm, and the physiological saline solution composed
of 0.90 wt % sodium chloride was poured until the surface level
became equal to the upper surface of the glass filter. Then, a
sheet of filter paper having a diameter of 90 mm was put on the
glass filter. Then, the measuring device was placed on the filter
paper and the solution was absorbed under a load for about 1 hour.
After one hour, the weight W.sub.b(g) of the device was measured
after lifting the measuring device.
[0162] Then, the absorbency under pressure was calculated according
to the following Equation from the weights of W.sub.a and
W.sub.b.
Absorbency under Pressure (g/g)=[W.sub.b(g)-W.sub.a(g)]/Weight of
Absorbed Polymer (g)
[0163] The test results are shown in Table 3.
Experimental Example 5. Absorption Rate
[0164] The absorption rate was measured for each of the
superabsorbent polymers prepared in Examples 1 to 3, Comparative
Examples 1 to 3 and Reference Examples 1 to 7. 50 mL of 0.9% saline
and a magnetic bar having a size of 20*5 mm were added to a 100 mL
beaker and stirred at 600 rpm. When a vortex is uniformly formed to
an extent that the vortex is almost in contact with the magnetic
bar, 2.+-.0.01 g of the superabsorbent polymers prepared in Example
1 and Example 2 and Comparative Examples 1 to 3 were added to the
formed vortex, and at this time, the time was measured
simultaneously. The time measured until the vortex disappeared and
thus the surface of the solution was completely level was defined
as the absorption rate.
[0165] The test results are shown in Table 3.
Experimental Example 6. Permeability
[0166] The permeability was measured for each of the superabsorbent
polymers prepared in Examples 1 to 3, Comparative Examples 1 to 3
and Reference Examples 1 to 7. About 10 mL of 0.9% saline was added
to a cylinder having a diameter of 20 mm having a glass filter and
a valve, and 0.2.+-.0.0005 g of superabsorbent polymers classified
into sizes of #30 to #50 were added. Thereafter, additional saline
was added so that the total amount of 0.9% saline was 50 mL. After
the superabsorbent polymers were sufficiently swollen for 30
minutes, the piston to which the mesh was attached was placed in
the cylinder, and a pressure of 0.3 psi was applied. After 1
minute, the valve at the bottom of the cylinder was opened, and the
time (in seconds) during which 20 mL of saline passed through the
gel bed from the upper line to the lower line was measured.
[0167] The test results were shown in Table 4 below.
Experimental Example 7. Anti-Caking Efficiency
[0168] The anti-caking efficiency was measured for each of the
superabsorbent polymers prepared in Examples 1 to 3, Comparative
Examples 1 to 3 and Reference Examples 1 to 7. First, the weight of
a Petri-dish having a diameter of 9 cm was measured and recorded
(W1). Thereafter, 2.+-.0.01 g of a sample was added to the
Petri-dish in order to evenly distribute the sample. The Petri-dish
was placed in a constant temperature and humidity chamber
maintaining at a temperature of 40.degree. C. and a humidity of 80%
RH, and allowed to stand for 10 minutes. After 5 minutes, the
weight of the polymer dropped on the floor was measured and
recorded (S1). Then, the weight of the Petri-dish was measured and
recorded (S2).
Anti-caking efficiency (%)=S1/((S2-W1)+S1).times.100
TABLE-US-00003 TABLE 3 Absorbency Centrifuge under Absorption
retention pressure rate Anti-caking capacity (AUP) (sec) Efficiency
(%) Example 1 31.4 18.4 69 100.0 Example 2 31.8 16.4 75 100.0
Example 3 30.8 16.4 68 100.0 Comparative 32.8 18.6 81 0.0 Example 1
Comparative 31.6 17.3 83 0.0 Example 2 Comparative 31.9 16.7 71
100.0 Example 3 Reference 31.7 17.0 81 0.0 Example 1 Reference 32.1
17.2 83 0.0 Example 2 Reference 31.0 17.1 82 0.0 Example 3
Reference 31.6 17.7 92 0.0 Example 4 Reference 31.5 17.5 73 77.4
Example 5 Reference 31.8 18.8 89 0.0 Example 6 Reference 31.4 18.8
86 0.0 Example 7
TABLE-US-00004 TABLE 4 Permeability Before ball After ball milling
milling Example 1 18 20 Example 2 14 18 Example 3 14 18 Comparative
41 114 Example 1 Comparative 29 38 Example 2 Comparative 16 19
Example 3 Reference 55 44 Example 1 Reference 26 50 Example 2
Reference 27 43 Example 3 Reference 29 50 Example 4 Reference 15 22
Example 5 Reference 57 185 Example 6 Reference 51 74 Example 7
Experimental Example 8. Measurement of Particle Size of
Superabsorbent Polymer
[0169] The particle size was measured for each of the
superabsorbent polymers prepared in Examples 1 to 3, Comparative
Examples 1 to 3 and Reference Examples 1 to 7. The particle size
was measured in accordance with EDANA recommended test method No.
WSP 220.3. The superabsorbent polymers were classified into 850
.mu.m, 600 .mu.m, 300 .mu.m, 150 .mu.m and pan mesh, and were
vibrated at an amplitude of 1.44 mm and a frequency of 50 Hz for 10
minutes, and then the content was measured as the residual amount
at the upper portion of each sieve.
[0170] The measurement results are shown in Table 5 below.
TABLE-US-00005 TABLE 5 Particle size ~#20 #20~#30 #30~#50 #50~#100
#100~ Example 1 0.43 32.80 53.86 12.09 0.82 Example 2 0.42 27.81
54.06 16.09 1.62 Example 3 0.29 22.92 56.45 18.48 1.86 Comparative
0.56 31.31 54.24 12.50 1.40 Example 1 Comparative 0.94 36.46 53.84
8.41 0.35 Example 2 Comparative 0.43 27.70 53.96 16.27 1.64 Example
3 Reference 0.62 31.87 54.48 12.27 0.75 Example 1 Reference 0.73
29.73 56.20 12.61 0.74 Example 2 Reference 0.46 33.90 54.48 10.62
0.54 Example 3 Reference 3.81 40.91 48.36 6.62 0.30 Example 4
Reference 0.64 32.38 53.71 12.05 1.22 Example 5 Reference 0.45
29.53 59.01 11.01 0.00 Example 6 Reference 11.12 51.89 34.80 1.94
0.25 Example 7
[0171] It can be confirmed from the results of Experimental
Examples 1 to 8 that, the superabsorbent polymers prepared in
Examples 1 to 3 showed no occurrence of fouling in the blender or
lumps upon treatment with solution, compared to a conventional
superabsorbent polymer. Further, although CRC and AUP were
inevitably reduced as much as water was added, it was confirmed
that the attrition resistance, permeability, absorption rate and
anti-caking efficiency were improved.
* * * * *